1. Field of the Invention
The present invention relates to an improvement of making intercell connections in multi-cell storage battery.
2. Prior Art
Several methods for making intercell connections in multi-cell storage battery have been proposed. For example, U.S. Pat. No. 3,313,658 for A. Sabatino et al discloses an art of squeeze welding or butt welding, which makes intercell connection by utilizing Joule heat in the butt welding. Another art is the art of press-caulking disclosed in the U.S. Pat. No. 3,336,164 for J. H. Miller. The important purpose of these conventional art is to secure good electric connections of intercell connections and good sealing of the battery cells.
The former prior art, the U.S. Pat. No. 3,313,658 for Sabatino et al. discloses the art that connectors of neighboring cells of a battery are connected each other by connecting projections of the connectors, penetrating through an opening on the intercell partition wall of the battery by electrical butt-welding, in such a manner that lead fused by Joule heat fills gaps between the aperture and the projection and gaps between the connectors and the partition walls, thereby air tightly sealing the intercell connection parts.
The latter prior art, the U.S. Pat. No. 3,336,164 for Miller discloses the art that a projection of a lead connector is, after passing through an opening of an intercell partition wall, inserted into an opening of another lead connector, and the projection is secured by mechanical fitting to the opening of the another connector thereby making an air-tight sealing and fixing.
The former art of Sabatino has the problem that by means of welding heat, the peripheral part of the opening of the intercell partition wall made of synthetic resin is decomposed, thereby producing gases, which come into the sealing part of connectors and form undesirable blow holes, which causes leakage of electrolyte and poor conductivity of the intercell connection.
In order to remove such problem of the gas produced by decomposing of the resin parts, an improvement to provide a gas discharging opening is proposed in the U.S. Pat. No. 3,687,734 for D. Orlando et al. However, even with such improved construction, it is very difficult to substantially remove the undesirable effect of the decomposition to gas at the opening part of the partition wall.
Furthermore, the butt welding method has another shortcoming that, when the electric contact resistance between the two connectors to be welded to each other is reduced as the welding proceeds, the temperature at the butt-welded part does not rise any more, therefore, an insufficient welding is carried out. Such insufficient welding is difficult to detect by its appearance or tensile test. Such insufficient welding will result in break off defects during its usage after a lapse of time. Furthermore, what makes the matter more difficult is that the insufficient butt-welding can not be cured by the butt-welding method, since no necessary Joule heat is obtainable after once decreasing of the electrical resistance as a result of welding.
The latter method (caulking) of Miller has a problem of possible cracks of the connector due to mechanical strain, and it is a great problem that such cracks can not be detected from outside, and that the battery having such cracks is likely to results in undesirable temperature rise at crack part and further in a melt-off and further in an explosion defect, after receiving repeated shocks in automobile or the like.
A further method have been proposed in the U.S. Pat. No. 3,767,889 for Ichiro Sano et al. The art of Sano et al utilizes an inert-gas shielded welding method or plasma arc welding method utilizing an inert-gas plasma torch. The problem of this method is that a tungsten electrode must be always controlled so as to have a right position irrespective of its continuous comsumption. This control requires a special apparatus in automatic welding machines in automated production lines.